The present invention concerns marking any translucent synthetic material object, i.e. applying a symbol to that object for identifying and/or tracing it.
The symbol can include, for example, a serial number, a reference number or any other inscription relating to the characteristics of the object concerned, the treatment it has undergone or that it is to undergo.
The present invention is more particularly, although not necessary exclusively, directed to the situation in which the object is an ophthalmic lens.
To assure the identification and/or the tracing, i.e. the "traceability", of an ophthalmic lens, whether it is a mineral glass ophthalmic lens or an organic material (synthetic material) ophthalmic lens, and thereby to enable its characteristics to be determined at any time by a simple reading process, it is necessary to apply to it a symbol including all the required information, in encoded form or otherwise.
In the case of a mineral glass ophthalmic lens, or more generally any object made from such glass, for example the molding shells used to mold synthetic material ophthalmic lenses, it has been proposed to use an etching process, in particular a laser etching process.
This is the case, for example, in published French patent application N.degree.2 732 917 (application N.degree.95 04314 filed Apr. 11, 1995).
In the above French patent application, it is proposed to cause the beam from a YAG laser to interfere with a layer of a particular material, in this instance a cement capable of reacting with the glass, applied to the surface of the object to be treated beforehand for this purpose.
This has the advantage of combining the resulting etching with a coloration which, by increasing the contrast of the etching, facilitates and renders more accurate subsequent reading of the symbol obtained in this way.
In the case of marking mineral glass objects, it is therefore satisfactory.
However, although they may be acceptable for mineral glass objects to be used many times, for example molding shells for molding synthetic material ophthalmic lenses, the costs inherent in the use of a cement of this kind are less acceptable for synthetic material objects which are not re-used, for example the ophthalmic lenses themselves, because they represent an unnecessary increase in the overall cost of such items.
Moreover, no such cement is necessary in this case, an appropriate choice of its wavelength enabling the laser beam to react directly with the synthetic material.